This invention relates to the disposition of magnets on a rotor in a synchronous motor.
xe2x80x9cNew Technologies for an EV Motorxe2x80x9d published in Report S.9-2 of the Industrially-Applied Technology Conference of the Institute of Electrical Engineers of Japan in 1999 discloses the application of magnets with a V-shaped cross-section on the rotor of a synchronous motor. EV is an abbreviation of the term xe2x80x9cElectric Vehiclexe2x80x9d.
Magnets with a V-shaped cross-section have a larger surface facing the stator situated at an outside of the rotor than magnets having a semi-circular cross-section or those having a rectangular cross-section which are generally used in rotors. Increases in the surface area of this part increase a magnetic flux formed between the coils of the stator and the magnets of the rotor. In other words, the effective magnetic flux driving the rotor to rotate is increased. The magnet is buried in a core made of laminated magnetic steel plates and is not exposed on an outer periphery of the rotor.
When magnets are covered in this manner, a reluctance torque is easily generated between the stator and the rotor. The increase of effective magnetic flux as well as the increase of reluctance torque brings an increase of output power of the motor.
Magnets having a V-shaped cross -section are magnetized so that a surface facing an inner periphery of the rotor and a surface facing an outer periphery thereof have different polarity. Thus leakage flux is formed between the ends of adjacent magnets that have different polarity.
When the distance between the ends of the magnets and an outer peripheral surface of the core is small as in the case of this rotor, leakage flux is conspicuously large.
The leakage flux decreases the effective magnet flux that drives the rotor and thus the driving efficiency of the rotor is adversely affected by leakage flux.
It is therefore an object of this invention to reduce leakage flux in a rotor provided with magnets of V-shaped cross-section.
In order to achieve the above object, this invention provides a rotor for a synchronous motor, comprising, a rotation shaft provided in the center of the rotor and rotating together with the rotor,a plurality of magnets and a core made of a magnetic material which is fixed to the rotation shaft to retain the magnets.
Each magnet has V-shaped cross-section that is defined by an inner V-surface having an acute angle point, an outer V-surface having an acute angle point and an outward face facing outwardly and connecting the inner V-surface and the outer V-surface. Each magnet is disposed to cause the acute angle points of the inner V-surface and the acute angle point of the outer V-surface to be directed towards the rotation shaft, and is magnetized to cause the inner V-surface and the outer V-surface to have a different polarity Each magnet has dimensions to cause a second angle xcex2 to be greater than twenty percent of a first angle xcex1. The first angle xcex1 is an angle subtended between a first straight line connecting an intersection point of the outer V-surface and the outward face and the center of the rotor and a second straight line connecting the center of the rotor and the acute angle point of the outer V-surface. The second angle xcex2 is an angle subtended between the first straight line and a third straight line connecting an intersection point of the inner V-surface and the outward face.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.